Today's conventional control systems for diesel engines (or other internal combustion engines that use direct fuel injection) are “fuel-based”. In response to activity of the accelerator pedal, an engine control unit determines the quantity of fuel to inject. Downward action of the accelerator pedal causes the engine control unit to inject more fuel.
Typical fuel-based engine control calibrations utilize high excess air ratios which do not result in combustion that is sensitive to variations in in-cylinder conditions. In particular, the combustion is not sensitive to airflow mass, air fuel ratio, or exhaust gas recirculation (EGR) rate. For some modern diesel engines, fuel injection is adjusted based on airflow mass measurement to control soot in small regions of the operating range, but this control method is still primarily fuel-based.
U.S. Pat. No. 7,163,007 describes an “oxygen-based” combustion control system. For both lean and rich operating conditions, an estimated in-cylinder oxygen amount (oxygen mass) is used to determine fueling parameters. For transient operating conditions (rich-to-lean or lean-to-rich), in addition to current oxygen mass, an oxygen mass ratio between lean and rich is used to determine the fueling parameters.